1. Field of the Invention
The present invention is generally related to a hydrostatic propulsion system for a marine vessel and, more particularly, to a hydrostatic propulsion system that uses an infinitely variable valve to distribute pressurized fluid from a hydrostatic pump to a hydrostatic motor as a function of a selected parameter, such as engine speed or throttle position or both.
2. Description of the Prior Art
Many different types of marine propulsion systems are well known to those skilled in the art. Some propulsion systems use gasoline powered internal combustion engines while others use diesel engines. It is known that a marine propulsion system can incorporate a hydrostatic pump, driven by an engine, in combination with a hydrostatic motor attached in torque transmitting relation with a propeller shaft of a marine vessel.
U.S. Pat. No. 5,813, 887, which issued to Mark on Sep. 29, 1998, discloses a marine propulsion system. Referring to prior stern drive marine propulsion systems in which power is transmitted through an arrangement of clutches, bevel gears, and shafts to a propeller located between the water surface, the Mark patent discusses the disadvantages of the prior art systems, particularly when these systems are used in large commercial boats. The invention disclosed in the Mark patent provides an outdrive designed to surpass the horsepower and torque limitations set by prior art systems. In order to meet these objectives, the outdrive is designed to incorporate a multi-strand roller chain drive, replacing the conventional bevel gear arrangement. Using a chain drive in this application serves to increase durability of the drive while keeping the outer casing streamlined. The system uses a variable displacement pump driven by an engine. The pump is connected in fluid communication with a hydraulic motor that provides the torque to drive a propeller shaft.
U.S. Pat. No. 5,121,603 which issued to Widemann on Jun. 16, 1992, describes a device for pressure regulated variable displacement motors with RPM-dependent set pressure compensation. The hydrostatic system includes a variable displacement hydraulic motor whose absorption volume is adjusted by a pressure regulator, depending on the RPM's generated by the power source driving the system. The apparatus enables the variable displacement motor to fully utilize the drive power available from the power source over a range of operating speeds.
U.S. Pat. No. 3,660,975, which issued to Martin et al on May 9, 1972, discloses a hydrostatic transmission system in which there is provided an automated pump displacement control, a manual override device for overriding the displacement control to keep the pump displacement at a low level, and a device sensitive to pump inlet pressure to render the override device inoperative when the pump inlet pressure exceeds a predetermined value.
U.S. Pat. No. 3,685,286, which issued to Lee on Aug. 22, 1972, describes a fluid control valve. The valve has a pair of spool closure members which are slidable in unison to control flow between associated pairs of ports in response to relative movement between a pair of control elements on the valve. The relative movement causes axial displacement of actuators which engage an abutment secured to the spools, the abutment being biased into contact with the actuators.
U.S. Pat. No. 3,672,166, which issued to Isaac on Jun. 27, 1972, discloses a variable ratio hydrostatic transmission which comprises a hydraulic motor as well as a pump of which the cubic capacity is regulated by a mechanism that is sensitive to the pressure of liquid. This liquid is supplied by a pressure regulator on the movable member of which act, in the sense tending to increase the pressure, a force increasing with the speed of the pump and, in reverse sense, a force increasing with the resistant couple applied to the motor and a force proportional to the pressure. The transmission is used in automobiles.
U.S. Pat. No. 5,094,077, which issued to Okada on Mar. 10, 1992, discloses a hydrostatic transmission with interconnected swash plate neutral valve and brake unit. The transmission system axle driving apparatus is used for changing the speed of a vehicle which includes a hydraulic pump, hydraulic motor, and braking unit. Neutral valves at an open position are automatically returned to a closed position with the operation of a brake controller. This allows the vehicle to be started at slow speed but not abruptly.
U.S. Pat. No. 4,215,546, which issued to Hager et al on Aug. 5, 1980, describes a hydrostatic transmission control system which includes a variable displacement pump driving a constant displacement motor arranged in a hydraulic circuit having a controlled by-pass valve interconnected for position the pump swash plate in two established positions corresponding respectively to a stand still position or a full speed position of the motor. A thermal sensitive element is coupled to the valve control spool for bypassing the flow of the pump in the event of motor jamming.
U.S. Pat. No. 5,588,294, which issued to Sakakura et al on Dec. 31, 1996, describes a hydrostatic transmission that is constructed so that a check valve and a relief valve are made as compact as possible to supply oil to a closed circuit for connecting a hydraulic pump and a hydraulic motor, and to regulate maximum pressure in the closed circuit. A check valve and a relief valve are contained in a valve casing. A valve body of the relief valve is disposed opposite to a valve body of the check valve. A relief spring of the relief valve is retained by a cover detachable mounted to an open end of the valve casing, thereby facilitating pressure setting of the relief valve. The valve body of the relief valve is contained in a relief valve casing slidably disposed in the valve casing. A plunger, capable of urging the check valve in the opening direction via the relief valve casing, is provided in the cover, thereby enabling the check valve to be manually opened.
U.S. Pat. No. 5,168,703, which issued to Tobias on Dec. 8, 1992, describes a continuously active pressure accumulator power transfer system for a vehicle. It comprises an engine, a pump driven by the engine, a main pressure accumulator maintained at a substantially constant fluid pressure and a fluid volume by the pump during operation, a fluid motor for propelling the vehicle which is supplied with driving fluid pressure from the pressure accumulator and auxiliary units for operating the vehicle. The auxiliary units are also operated by fluid pressure from the pressure accumulator. The fluid motor and the auxiliary units are operated directly by fluid pressure from the accumulator without any direct connection with the engine.
The patents described above are hereby incorporated by reference in this description.
Although many different types of hydraulic propulsion systems are known to those skilled in the art, they are not generally used in marine applications in conjunction with pleasure craft or small commercial craft. Certain working vessels use hydraulic propulsion systems. However, hydraulic propulsion systems exhibit certain disadvantages which have inhibited their use in conjunction with pleasure craft or small commercial craft. For example, by their nature, hydrostatic propulsion systems typically have significantly lower operating efficiencies than conventional mechanical systems. Since hydrostatic propulsion systems use an engine as a prime mover, a hydrostatic pump driven by the engine, and a hydrostatic motor to drive a propeller shaft, the total system suffers from the combined inefficiencies of the hydrostatic pump and hydrostatic motor in addition to the other inefficiencies common to systems of this type. As a result, hydrostatic propulsion systems generally lack the acceleration capabilities that are particularly desirable in marine pleasure craft or small commercial craft. Therefore, although hydrostatic propulsion systems exhibit certain highly advantageous characteristics, they are not generally used in pleasure craft or small commercial craft because of the adverse effect of decreased efficiency on the operating characteristic of the propulsion system and the marine pleasure craft or small commercial craft with which it is used.
It would therefore by highly beneficial if a hydrostatic propulsion system could be configured in such a way that a marine pleasure craft or small commercial craft could take advantage of certain inherent beneficial characteristics of hydrostatic propulsion systems while avoiding certain inherent disadvantages such as reduced acceleration.